Fishtek Tagalog

Combine soy sauce, calamansi, pepper, and garlic. Marinate fish in this mixture for 30 minutes. (The fish absorbs a lot of flavor so don't overdo the marinating.)

Heat a nonstick skillet over medium heat then add a couple of swirls of oil, just enough to coat the bottom of the pan lightly. Once oil is hot, remove fish from marinade and fry, waiting until a touch golden on each side and cooked through. Do not overcook. Set fish aside.  

Add a couple more swirls of olive oil to the pan and fry onions until golden and caramelized.  When onions have reached your desired degree of softness, add remaining marinade to the pan and cook until everything bubbles up. Simmer rapidly for a minute or two. You want to make sure the marinade cooks thoroughly since it was in contact with the raw fish.

Once sauce is done, return fish to the pan and toss gently with the onions and sauce, just enough to warm fish. Serve immediately.